The present invention relates in general to the chemical treatment of sewer and other types of pipes, and, more particularly, to a method and apparatus for generating a chemical foam for filling or coating the interior of such pipes.
Various types of chemicals are used in sewer and other types of pipes to kill tree roots and other types of organic matter which can cause blockage of the pipe if their growth is not periodically controlled. Chemical treatments of this type are most effective if the chemical remains in contact with the roots for a period of time. In general, extended contact of the chemical with the organic matter can be achieved by placing a plug in the pipe and then filling the downline portion of the pipe with the chemical in liquid form or as a foam: While this type of treatment can be effective for smaller diameter pipes, it is typically uneconomical to use this technique on larger diameter pipes because of the large volume of chemical or foam needed to fill the pipe. Thus, on larger diameter pipes it is desirable to coat the inner wall of the pipe with a chemical foam which will cling to the inner wall for the desired time period.
Various methods are available to generate the foam which contains the chemical used to kill the organic matter in pipes. Typically, the chemical is mixed with a foaming agent and is then pumped into the pipe being treated through a flexible conduit which has an application head or spray nozzle connected at its end. Examples of application systems of this type are disclosed in U.S. Pat. No. 4,944,320 to Waite et al. and U.S. Pat. No. 3,880,176 to Horne. One problem with systems of this type is the difficulty in controlling the consistency of the foam at the outlet nozzle. Because the foam is pumped into the pipe through the conduit which may be several hundred feet in length, by the time the foam arrives at the outlet nozzle, it often has a far different consistency than when it was initially produced. In some instances, the foam discharged by the nozzle has considerably less entrained air than when it was initially formed. A larger amount of foam and chemical is then required to completely fill the pipe or coat the inner wall surface. In addition to the added expense resulting from producing this additional foam, the foam itself may have a liquid consistency which results in its collapse before it has remained in contact with the organic matter for the desired length of time. Less than completely effective treatment may thus result from the pumping of such foam into the pipe being treated.
A need has thus developed for a system which can be used to produce and apply a chemical foam having a desired consistency at a remote location within a length of pipe.